It is well known that phenol and water form an azeotrope which is difficult to separate. Where it is desired also to remove substantial amounts of inorganic salts from mixtures of phenol and water, the process parameters become perhaps even more complicated.
In Volume 44, No. 2 of Chemical Engineering Progress (1948), Bogart and Brunjes reported, in "Distillation of Phenolic Brines", experiments on separations of a phenol-water-salt mixture of a type obtained from the neutralization of sodium phenate with hydrochloric acid. They observed that sodium chloride in relatively high concentrations performed a function similar to that of a selective solvent in extractive distillation, making feasible (although still difficult) the recovery of phenol from relatively weak solutions. According to Bogart and Brunjes, the typical phenol-water-salt mixture from the neutralization of sodium phenate will contain about 6.7% phenol. Furthermore, in the process they employed to enhance the separation of phenol, the azeotrope composition containing 9.2 weight percent phenol was found to provide the "maximum enrichment".
In U.S. Pat. 3,829,509, Charles et al disclose the addition of calcium or magnesium chloride to an aqueous solution of phenol and hydrogen chloride to enhance the separation of the phenol and the hydrogen chloride by distillation. The high concentrations of calcium or magnesium chloride apparently increase the relative volatility of the hydrogen chloride and the phenol. The system is different from that of the inventors herein, in that the present system treats a waste water system from a phenol plant, which includes substantial amounts of sodium sulfate.